Regiospecific arene C-H self-hydroxylation in pentadentate ligand via activation of atmospheric dioxygen utilizing Co(II) precursors under ambient reaction conditions: Experimental and DFT optimized studies

Abstract

The activation of dioxygen on redox-active metal centres is an important area of study in bioinorganic chemistry. One of the key challenges in this field is the activation of atmospheric dioxygen under ambient conditions. In this study, we report the ligand-induced activation of atmospheric dioxygen using cobalt(II) precursors and the oxygenation of arene C-H bonds within a pentadentate ligand under ambient conditions. Herein, a novel pentadentate ligand BPMAP-H = (E)-2-(bis(pyridin-2-ylmethyl)amino)-N-(2-(phenyldiazenyl)phenyl)acetamide) having carboxamide and azo donor groups was synthesized and utilized for dioxygen activation. A number of cobalt(II), precursors with BPMAP-H provide [Co(III)BPMAP-O]ClO4 complex Co-1 with oxidation at the metal centre and phenyl ring oxygenation in ligand backbone. Both the ligand BPMAP-H and complex Co-1 were well characterized by UV-visible spectroscopy, IR spectroscopy, 1H NMR, 13C NMR, 13C DEPT-135, HRMS, and single-crystal XRD. Several controlled experiments and DFT calculations were performed for mechanistic investigation and the in-situ formed cobalt(III)-superoxide was characterized as a key intermediate with the help of EPR studies.